UN commission downplays claim Syria rebels used sarin
The UN Commission of Inquiry on Syria has sought to distance itself from comments made by one of its members that there was evidence of the nerve agent sarin being used by rebels.
Carla Del Ponte said testimony from victims and doctors had given rise to "strong, concrete suspicions but not yet incontrovertible proof".
But the commission stressed that it had not reached any "conclusive findings".
The US said it had no information to suggest rebel fighters had used sarin.
In recent weeks, Western powers have said their own investigations have found evidence that government forces have used chemical weapons.
In an interview with Swiss-Italian TV on Sunday, Ms Del Ponte, who serves on the Independent International Commission of Inquiry on Syria, said: "Our investigators have been in neighbouring countries interviewing victims, doctors and field hospitals.
"According to their report of last week, which I have seen, there are strong, concrete suspicions but not yet incontrovertible proof of the use of sarin gas, from the way the victims were treated."
Sarin, an extremely potent chemical nerve agent, is colourless and odourless. The use of chemical weapons is banned by most countries.
Ms Del Ponte did not rule out the possibility that troops loyal to President Bashar al-Assad might also have used chemical weapons, but said further investigation was needed.
On Monday, the Commission of Inquiry headed by Brazilian Paulo Sergio Pinheiro, issued a statement "to clarify that it has not reached conclusive findings as to the use of chemical weapons in Syria by any parties to the conflict".
"As a result, the commission is not in a position to further comment on the allegations at this time," it said, adding that it would present its findings to the Human Rights Council on 3 June.
The BBC's Imogen Foulkes in Geneva says the UN was clearly taken by surprise at Ms Del Ponte's comments.
The use of chemical weapons has been described as a "game-changer" - something that could trigger international military intervention - and UN diplomats know evidence of it will have to be cast-iron before they can accuse either side, our correspondent adds.
US officials in Washington also played down Ms Del Ponte's comments.
"The fact of the matter is - as we have said, and I have said many times - that we are highly sceptical of suggestions that the opposition could have or did use chemical weapons," White House spokesman Jay Carney told reporters.
"We find it highly likely that any chemical weapon use that has taken place in Syria was done by the Assad regime. And that remains our position."
Last week, the US and UK said their own investigations suggest government forces had used chemical weapons, including sarin. British Defence Secretary Philip Hammond said the evidence was quite compelling, but that it would need to be incontrovertible before the case for an international response could be made at the UN.
The main opposition alliance, the National Coalition, warned against the use of chemical weapons by either side, but said it believed only government forces had the capability.
"The coalition condemns all use of chemical weapons, whoever uses them, and it will pursue its investigation and collect evidence on this issue to present to the international commission of inquiry," a statement said.
"If the inquiry proves that any party other than the Syrian regime has used chemical weapons, the coalition will take all legal and appropriate measures, whoever the party is and whatever the reason or motive for the usage might be."
A special UN team, appointed by Secretary General Ban Ki-moon to look specifically at possible use of chemical weapons, is ready to enter Syria. However, it wants unimpeded access to all areas of the country, to which the government has so far not agreed.
In a separate development on Monday, two rockets fired from Syria exploded on the Israel-occupied Golan Heights, without causing casualties or damage, the Israeli army said.
The rocket-fire came amid heightened tensions following a series of Israeli air strikes on targets in southern Syria on Friday and Sunday.
Israeli security sources said Sunday's attacks were aimed at preventing the transfer of advanced Iranian-made missiles to the Shia Islamist movement, Hezbollah, in neighbouring Lebanon.
Syria's government acknowledged that military installations were hit at three different locations between Damascus and the Lebanese border. TV footage of the aftermath showed huge destruction, and unofficial estimates put the number of Syrian soldiers killed at between 40 and 300.